Why did 9/11 create the TSA when earlier plane attacks didn't lead to the same changes?

I recently realized TSA didn't exist before 9/11, which made me curious about how airport security worked before it.

The US had already experienced major hijackings in the 1960s and 1970s, and attacks like Pan Am Flight 103 in 1988. Yet airport security never became a large federal system like TSA.

What interests me is not just why TSA was created after 9/11, but why previous incidents didn't lead to a similar transformation.

Was it mainly because 9/11 introduced a completely different kind of threat, or were there bigger institutional and political reasons why airport security stayed the way it was for so long?